Device and method for sorting out metal fractions from a stream of bulk material

ABSTRACT

The invention relates to a device and a method for blowing out metal fractions from a stream of bulk material that is conveyed by bulk material means. The device comprises blow-out nozzles which are located on a drop section, and which are arranged along a width-wise extension of the stream of bulk material, for blowing against individual particles of bulk material in order to modify the trajectory in such a way as to produce a second sub-stream that branches off. The blow-out nozzles can be controlled according to the sensor coil scanning results relating to the bulk material particles. A plurality of sensor coils is provided underneath an essentially horizontal section of the stream of bulk material in the form of an LC oscillating circuit. Said sensor coils are provided for detecting the eddy currents that are induced. Optoelectronic means are also provided for determining the blow-out position and for determining the location of each of the particles of bulk material.

PRIOR APPLICATIONS

[0001] This application bases priority on International Application No.PCT/DE01/00108, filed Jan. 12, 2001, which in turn bases priority onGerman Application No. DE 100 03 562.0, filed Jan. 27, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a device and method for sorting out orextracting metal fractions from a bulk material stream.

[0004] 2. Description of the Prior Art

[0005] It is necessary to sort out or separate metal fractions from themost varied bulk material streams. In the simplest case they areconstituted by crown corks of beer bottles and aluminum parts from abroken glass bulk material stream. However, it is also necessary to sorton the basis of their different metal and non-metal fractions,non-homogeneous bulk material streams, e.g. shredded car parts. Inparticular, the stainless steel fraction has to be separated from otherfractions. In the same way as nonferrous metals, stainless steel is notvery ferromagnetic.

[0006] Such a method is described in DE-A1-35 13 664, in which aninductance-variable detector coil on a refuse chute controls acompressed air nozzle, which blows away nonferrous metals. Quite apartfrom the limited local resolution, which is just sufficient for thedetection of aluminum cans, the problem arises that varying inductancechanges for different materials and also different object sizes do notallow clear information to be provided with regards to the optimumblow-out point. It is always only possible to blow out a specificfraction and not, if different compositions exist, the smaller fractionfor whose blowing out only reduced costs are involved.

[0007] It is impossible to blow out non-metals, although this is highlydesirable in the case of crushed car scrap.

[0008] As a result of saturation effects, particles bringing about astrong inductance change can desensitize the coil for such a long timethat it is necessary to accept a significant level of incorrect sortingor extremely slow feed rates.

[0009] Methods of the type described, e.g. in DE-A1-40 14 969 areconsequently not very suitable for correctly detecting metal and for thedifferent handling of different metal fractions.

[0010] The parallel detection of both the color and the presence ofmetal requires a considerable amount of time which, as described inDE-A1-40 17 129, gives rise to slow bulk material conveying rates.

[0011] Other proposals, such as e.g. those of DE-A1-42 35 956, in whichthe fine surface structure of the materials are determined by bombardingwith electromagnetic waves, are much too complicated and costly duringevaluation, and require a time-consuming logic consideration. Inaddition, proposals have already been made for increasing the separationefficiency of material mixtures, such as e.g. in German utility modelDEU-93 09 786.

[0012] Finally, DE-A1-40 17 274 describes an apparatus for detecting andseparating metal particles, in which different down pipes are providedwith detector coils, which in each case control a flap mechanism fordeflecting fluid bulk material. In the case of shredded material, e.g.car scrap, unavoidably there are certain parts which are well above thenominal size, and which would immediately block such pipes. However,even in the case of bulk material such pipes tend to become blocked.

[0013] It is also desirable, as a function of the bulk material to besorted, to be able to readjust the separation efficiency in order totake account of different bulk material prerequisites and enable thesorting out of the in each case desired fractions.

[0014] Thus, it is e.g. known that there can be considerable differencesin shredded car scrap as a function of the country of origin. Whereas,European car scrap contains a large amount of light alloys and plasticparts, in the scrap from U.S. cars, there are far more stainless steelparts, whose sorting out is correspondingly worthwhile.

[0015] It is also known that the size and shape of the parts to besorted are dependent on the nature of the shredding machine, quite apartfrom the materials used in the vehicles. However, once a first batch hasbeen supplied by a particular preprocessing plant, it is generally to beassumed that over a long period (the next years), parts with a similarsize and shape will arrive and the sorting parameters when operating thesorting apparatus, consequently, remain substantially the same.

[0016] The problem of the invention is to provide a method and apparatusfor sorting out such metal fractions, sorting out having to take placerapidly and also reliably in the case of larger parts.

[0017] Specifically, in the case of larger parts, it is necessary tocontrol the blow-out nozzles in such a way that the parts are correctlyblown out, because too sort or too early blowing (such as arises withlarge objects through a premature response of the prior art metaldetectors) will not lead to the parts being correctly brought into a newtrajectory. In the case of shredders, there are also many elongatedparts, which are difficult to blow out.

SUMMARY OF THE INVENTION

[0018] According to the invention, this problem is solved by thefeatures of the main claim. The subclaims provide advantageousembodiments of the invention.

[0019] It is in particular advantageous that as a result of theinventive arrangement of an electromagnetic sensor below advantageouslya horizontally directed conveyor belt, it is not only possible todetermine the digital signal metal (YES/NO), but also a signal patternfrom whose details, particularly its edge rise, conclusions can ifnecessary be drawn concerning the size and the material of theindividual parts.

[0020] As a result of the position of the essentially flat parts on theconveyor belt, it is possible to consider the distance between the masscenter and the sensor to be identical for all the parts.

[0021] By means of the sensor described in the second part of thedescription relative to the drawings, it is possible to generate eddycurrents in a metal part to be separated, particularly an aluminum orstainless steel part, which in turn builds up a magnetic field acting inopposition to the excitation field. As a result of the buildup of thefield, but in particular through line losses to which the eddy currentsare exposed in the metal, an energy loss is brought about in thefield-generating sensor, which as damping of said oscillator is in orderfor the size, spacing and dimensions of the object. The individualparticles to be sorted out are slightly heated by the eddy currents.

[0022] Admittedly, use has already been made of the generation ofopposing fields by eddy currents, induced by very strong fields in orderto deflect from the trajectory in which the rotational fields arise, butthis deflection is determined by the geometry of the object and the eddycurrents flowing in said object and less by the actual material, and isnot of an optimum nature in its directional component.

[0023] However, the invention “misses” the particle and controls ablow-out nozzle bar, which provides the particle with a suitable airstream for ejection during a drop section, which e.g. follows ahorizontally directed conveyor belt. Thus, for the selected particles analways identical trajectory is much more reliably ensured than by a verystrong field, which induces eddy currents in all the objects with adifferent intensity for ejection purposes.

[0024] In addition, the invention makes it possible to mathematicallyevaluate the data detected for an object, namely the size, the strengthof the eddy current caused (the steepness of an edge rise in the signalpattern enabling conclusions to be drawn thereon), in which the strengthof the back-indication of the object, i.e. either its weight or in thecase of comparable weights of the particles its material, 1) can bedetermined by mathematical integration over the surface area of a“peak”, or which can be easily implemented from the apparatus standpointin the plant by, 2) can be taken into account by modifying the distancefrom the changed sensor and the bulk material stream, so that in bothcases, the response limits for separation can be easily changed.

[0025] A major advantage is provided by the optional, opticaldetermination of the particles on the belt or at the start of the dropsection, because it provides the possibility of more precise positionalinformation to blow against the centers of gravity of the particles bymeans of the air nozzles which are provided with precisely determinedaction points and much more densely provided than the coils, so as tobring about an optimum trajectory change.

[0026] Through a plurality of sensors, which can be juxtaposed at rightangles to the bulk material stream, it is possible to monitor the entirebulk material stream and provide a further metal/no metal informationconcerning the optically detected objects, and in the case of anadequate separation efficiency, to permit a decision to be madeconcerning the nature of the metal by means of the object size andsensor information.

[0027] As the field distribution of any LC sensor coil drops stronglytowards the edge, it is proposed that there are at least two mutuallydisplaced rows.

[0028] The invention also proposes, in addition to the sensorsequidistantly spaced with respect to the bulk material stream, theprovision of further sensors with different spacings with respect tosaid stream, so as in this way to detect fractions with significantlydifferent response ranges in the bulk material stream, and consequentlypermit the sorting out of certain fractions between the upper and lowerlimits.

[0029] However, it is also possible to provide additionaloptoelectronics sensors, which can qualify the signals obtained from theelectromagnetic detection with optoelectronically detected signals, i.e.for example the size and color of the object.

[0030] Another advantage of the invention is the possibility of logicalreversal, i.e. either the blowing out of utilizable metal fractions orthe blowing out of utilizable plastic fractions, as a function of whichprovides the desired, marketable fraction in the most type-pure form.

DESCRIPTION OF THE DRAWINGS

[0031] Further features and advantages of the invention can be gatheredfrom the attached drawings, wherein:

[0032]FIG. 1 shows a diagrammatic representation of a sorting apparatusaccording to the method of the invention; and

[0033]FIG. 2 shows the geometry of the coil arrangement for the sortingapparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] As is diagrammatically indicated in FIG. 1, the apparatus hasbulk material-conveying means 10, namely a conveyor belt, to which isoptionally connected a gravity chute 12 in the first part of a dropsection for parallelizing the individual particles.

[0035] In free fall, the individual objects are then detected by a linecamera 14, which line-wise images the object flow and passes the signalsthereof to an electronic system, which detects with an evaluating meansa plurality of lines of individual objects and subdivides said objectsinto color, and possibly shape classes, and in particular, for eachobject determines the sensor information in questions from the detectorcoils 18 in order on the basis thereof to supply a positionally preciseblow-out command to a row of blow-out nozzles 20.

[0036] Thus, the blow-out nozzles 20 can also blow-out elongatedobjects, and those for which the sensor coils 18 did not respond, inthat the trajectory is modified, e.g., to the right behind a partition22.

[0037] As the sensor coils 18 have a worse response behavior at the edgethan in the center, it is proposed that they be arranged in two,mutually displaced rows. The time displacement on response (from top tobottom in FIG. 2) to bulk material particles can be compensated withoutgreat expense by signal processing means on the way to the controlelectronics.

[0038] Due to the fact that the plurality of sensor coils 18 in the formof LC resonant circuits is located under a substantially horizontalportion of the bulk material stream, has the advantage that the spacingvariable with respect to the coil, which has a very marked effect on theresult, varies to a minimum degree between individual objects, becausethey generally come with their center of gravity closest to the conveyorbelt. The resonant circuits induce high frequency eddy currents, whosepresence gives rise to a damping of the coils 18, which indicates thepresence of a metal particle, but not yet suitable for determining theblow-out position. Even a plurality of sensor rows only supplies thisinformation in an inadequate form, so that additional optoelectronicmeans, namely the line camera 14 are provided for determining theposition of each bulk material particle. A lighting means 16 can beprovided in transmitted light or in incident light. The camera 14,lighting system 16 and blow-out nozzles 20 can also be located on thetrajectory side opposite to that shown in FIG. 1, or two or more camerascan be used for observing both the front and rear. Such a variant isparticularly suitable for the correct sorting out of compositematerials, such as increasingly occur in car scrap.

[0039] Thus, in the case of composite materials, it is possible todetect whether e.g. there are hoses with metal clips, so that apredetermination can take place in the software of the plant regardingtheir supply to one of the fractions. It can be desirable either as aresult of the small metal part to supply them to the metal fraction ordue to the preponderant rubber part to the nonferrous fraction.

[0040] It is advantageous to operate very small sensor coils 18 with ahigh frequency of approximately 100 kHz. Thus, as shown in FIG. 2, forcoil dimensions of 35 mm and a center-to-center spacing in a row of 50mm, there is a sensor grid scale of 25 mm, i.e. an overlap of in eachcase 10 mm on each side of the coil, which corresponds to the hatchedouter area.

[0041] With a working width of e.g. 1200 mm and a product speed of 2.0m/s, in the case of 48 sensors per line and a scanning rate of 0.2 kHzwith a particle size of 50 mm, there are 8 measured values per particle,which readily permits an evaluation of the signal edges.

[0042] Image processing can then improve the vertical resolution of themetal sensor means from 10 to 1 mm, because here working can take placewith a grid scale of 0.5 mm and a scanning rate of 2 kHz.

[0043] The sensor coils 18 are arranged in a pot emitting the flux linesin closely concentrated manner upwards through an open end side andwhich is constructed in one piece with a centrally, perpendicularlypositioned ferrite core 24 (diameter approx. 10 mm).

[0044] The operating voltage is advantageously 20 to 30 V DC, and foradjusting the response sensitivity, besides a potentiometer, there aremeans for the displacement of the sensor coils 18 of a line away fromthe bulk material stream at different distances therefrom.

[0045] From the apparatus standpoint, this is brought about by means ofa vertical drawer precisely adjustable by means of spindle drives for ineach case one line of sensor coils 18, displaceable inprogram-controlled manner more rapidly by electromagnets in at least twodifferent planes.

[0046] The signals received by each coil are supplied via a demodulatorto a trigger circuit for signal evaluation with respect to the signallevel.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:
 10. A method for sorting out metalfractions from a bulk material stream, the steps of the methodcomprising: a) providing a bulk material conveying means whereinparticles of the bulk material stream move along the conveying means ina predetermined arranged width; b) providing a drop section along adistal end of the bulk material conveying means; c) providing a set ofsensor coils positioned below the bulk material conveying means; d)scanning the bulk material stream particles by the set of sensor coils;e) providing a plurality of blow-out nozzles positioned proximal to thebulk material conveying means drop section, each blow-out nozzle beingindividually controllable as a function of the scanning results of thesenors; f) determining an edge rise of a damping of in each case one ofa multiplicity of high frequency fields induced by LC resonant circuitsformed on a horizontal portion of the bulk material stream; g)evaluating each edge rise; and h) controlling at least one of theplurality of blow-out nozzles for deflecting the particles into abranched partial stream by selectively blowing against individual bulkmaterial stream particles.
 11. The method of claims 10, furthercomprising the steps of: a) providing an optical determination devicepositioned at a bottom portion of the bulk material conveying means dropsection; b) obtaining optically determined data from the opticaldetermination device; and C) correlating a determined electromagneticcharacteristic of each bulk material stream particle with the opticallydetermined data such that the particle can be identified.
 12. The methodof claim 11, wherein the optically determined data obtained by theoptical determination device is high resolution color data.
 13. Themethod of claim 11, wherein the optical determination device is at leastone line camera.
 14. The method of claim 10, wherein the bulk conveyingmeans is a conveyer belt.
 15. The method of claim 10, wherein the bulkmaterial conveying means drop section is a gravity chute.
 16. The methodof claim 10, wherein the set of sensor coils form the LC resonantcircuits.
 17. An apparatus for sorting out metal fractions from a bulkmaterial stream, the apparatus comprising: a) a conveyor belt having adistal end for moving the bulk material stream along a pathway; b) adrop section having a bottom end and located at the conveyor belt distalend; c) at least one blow-out nozzle positioned directly below the dropsection bottom end for blowing against individual particles of the bulkmaterial stream and for separating the particles into a second branchedstream; d) a plurality of sensor coils disposed below a horizontalportion of the conveyor belt for forming a set of LC resonant circuits,the plurality of sensor circuits detecting induced eddy currents in theparticles of the bulk material stream moving along the conveyor belt; e)calculating means for evaluating a signal pattern of the induced eddycurrents and for determining the position of the at least one blow-outnozzle; and f) optoelectronic means for determining the location of eachparticle of the bulk material stream.
 18. The apparatus of claim 17,wherein the plurality of sensor coils operate with a high frequency ofapproximately 100 kHz.
 19. The apparatus of claim 17, wherein theplurality of sensor coils are located within in potentiometer emittingflux lines upwardly through an open end side thereof.
 20. The apparatusof claim 19, wherein each of the plurality of sensor coils locatedwithin the potentiometer are constructed as one piece with a centrallyand vertically disposed ferrite core.
 21. The apparatus of claim 17,wherein the plurality of sensor coils are arranged in at least twostaggered lines at right angles to the bulk material stream.
 22. Theapparatus of claim 21, wherein the plurality of sensor coils in eachline are jointly displaced at different distances away from the bulkmaterial stream.
 23. The apparatus of claim 17, wherein the plurality ofsensor coils produce signals which are supplied by a demodulator of atrigger circuit.
 24. The apparatus of claim 17, wherein the plurality ofsensor coils are vertically displaced to the conveyor belt horizontalportion.
 25. The apparatus of claim 17, wherein the conveyor belt dropsection is a gravity chute.
 26. The apparatus of claim 17, wherein theoptoelectronic means is at least one line camera positioned below thedrop section bottom end.